The recording of data in binary form by means of alteration of a magnetic field on portions of a medium surface is well known in the art. Moreover, the use of rotating magnetic media such as in floppy diskettes and in rigid disk drives is widely practiced. Recording of data on magnetic media is accomplished by using a read/write head to polarize the magnetic fields of particles on a medium in one of two distinguishable orientations, such that a transition between such orientations indicates either a timing pulse or a data bit (one), and no transition at a data bit location indicates a no data bit (zero). To retrieve the written data, the disk is rotated past the read/write head such that the previously aligned fields induce currents in the read/write head corresponding to the previously recorded data. When there is a constant magnetic field, no indication of recorded data is produced. These general principles for recording and retrieving data from rotating magnetic media pertain to rigid (hard disk) media as well as to floppy disks. The most common field orientation scheme for recording data on rotating magnetic media is to cause consecutive fields to be polarized alternately in the direction of rotation of the medium and then opposite to such direction, such that passing a transition between two contiguous oppositely polarized areas over a read/write head gap induces a current through the read/write head coil which can serve as an indication of a data bit. A variation of this scheme to increase data capacity has been to orient the magnetic fields perpendicularly to the medium surface rather than across its surface. This method, also, operates by means of detecting the transition from one orientation to another to indicate a data bit.
Variations of these same principles for recording and reading magnetic media also apply to the use of magnetic tapes as well as to the magnetic strips on credit cards and similar data cards. In most cases, a transition between field states, as described above, is used to indicate a data bit (one) while a no transition, or steady state, is used to indicate a no data bit (zero).
A problem that has continued to plague users of magnetic data storage media has been that information contained on such media can be inadvertently erased, either by operator error when using the media or by accidentally placing the media within the influence of a strong magnetic field. Obviously, it would be desirable to have magnetically readable data that could not be erased. If such data could be combined on a medium surface with areas which could be written to and erased in a normal manner, even more benefit could be derived.
One method that is known in the art for placing permanent reference marks and the like on a magnetic medium is to remove the magnetic material from an area of the medium such that a magnetic field cannot be established thereon. An example of this is found in U.S. Pat. No. 4,961,123 issued to Godwin et al.. However, all such prior art techniques resulted only in the establishment of mechanical reference tracks, servo reference marks, or gross areas of intentional permanent random error. Prior to the resent invention, no means has been found for using this general technique to create actual data on a medium surface.
All of the prior art methods for placing data on a magnetic storage medium within the inventor's knowledge have resulted in data which can be erased either inadvertently or intentionally.
No prior art method for placing data on a magnetic storage medium to the inventor's knowledge has successfully produced data which cannot be erased magnetically. All successful methods for writing data to magnetic media have resulted in stored data which can be magnetically erased.